Sky News said marshalls were alerted to a passenger who had taken a long time in one of the plane's toilets. When he emerged, a marshall could smell smoke and asked the man what had happened.His alleged reply was: 'I was trying to set my shoes on fire.'

Two F-16 fighter jets from Buckley Air Force Base flew alongside the passenger plane for the final 40 minutes of its journey.A spokesman for the FBI in Denver declined to comment.